As optical communications have developed, it has become necessary to cause light transmitted through a single optical fiber to branch into a plurality of optical fibers, and to cause light transmitted through a plurality of optical fibers to be collected in a single optical fiber. Waveguides have been used for this purpose. For example, an outline of a waveguide is described in Japanese Patent Application Laid-Open No. H10-246838.
Meanwhile, optical fibers are generally fibers in which a naked optical fiber with a diameter of approximately 125 μm consisting of a core and cladding is protected by a covering with a diameter of approximately 250 μm. Accordingly, in cases where optical fibers are lined up side by side in a single row, the spacing of the cores is approximately 250 μm, so that the spacing of the light emission openings of the corresponding waveguide is also a pitch of approximately 250 μm.
In this case, however, the size of the waveguide is increased, so that the cost of the waveguide is increased by a corresponding amount. Accordingly, in order to make waveguides more compact, there have been attempts to strip the covering from the portions of the optical fibers facing the waveguide so that naked optical fibers are produced, and to line these optical fibers up in a single row so that the spacing is adjusted to approximately 125 μm, thus adjusting the spacing of the light emission openings of the waveguide to approximately 125 μm. Various methods have been proposed for this.
Typical methods are the methods described in Japanese Patent Application Laid-Open No. H10-246838 and Japanese Patent Application Laid-Open No. 2002-40284. In these methods, the covering is removed from the end parts of the optical fibers, and the naked optical fibers are fastened in V grooves formed at a pitch of 125 μm. In this case, the V grooves are formed by etching quartz, Pyrex (registered trademark), or the like.
As was described above, however, in cases where the covering is stripped from the end parts of optical fibers having a covering with an external diameter of approximately 250 μm and it is attempted to line up the optical fibers as naked optical fibers at a spacing of approximately 125 μm, there are problems in strength if the naked optical fiber portions are lengthened. Accordingly, the length of these portions is limited. Consequently, bending stress is generated in the naked optical fiber portions, and such stress causes damage. Furthermore, in the substrate in which the V grooves are formed, it is necessary to work quartz, Pyrex, or the like by etching with a high degree of precision, so that the problem of high cost also arises.